The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
There are numerous ways to classify or categorize automatic transmissions for motor vehicles. Perhaps the most popular and practical way relates to the overall speed ratio change structure. Given this criterion, planetary gear, continuously variable and dual clutch transmissions constitute the three currently most popular types.
Another way to classify automatic transmissions relates to their speed ratio shift configuration. Certain transmissions are classified as clutch-to-clutch transmissions meaning that each shift is accomplished by the release or disengagement of at least one clutch and the activation or engagement of at least one other clutch. This class of automatic transmissions includes most multiple planetary gear and all dual clutch transmissions.
In clutch-to-clutch transmissions, the manner of clutch engagement and disengagement, that is, how quickly engagement (or disengagement) begins after a command, the rate of engagement dE/dt (or disengagement dD/dt), and the time to full engagement (or disengagement), for example, are critical to the overall satisfactory transmission operation and performance which demands consistent and smooth shifts.
In clutch-to-clutch transmissions, to engage a clutch controllably, the piston actuating the clutch is moved to a point at which the full stroke of the clutch is completed. Thus, the clutch volume is completely filled with transmission or hydraulic fluid. After this “fill phase,” the torque transmitted by the clutch is then controlled by controlling the clutch fluid pressure.
Prior art clutch control systems rely on collecting indirect information and utilizing it after a shift has been completed to determine the required fill time and time to begin full clutch engagement. This approach is limited by the numerous calibrations that must be utilized to relate the available data to the fill volume and the slow convergence rate of this limited data which delays and adds uncertainty to the computation of the clutch fill time.
As the sophistication of clutch-to-clutch and other transmissions increases and their performance and fuel efficiency goals become even more demanding, controlled, that is, proper and desired engagement and disengagement of clutches in clutch-to-clutch and other transmissions is of increasing importance. The present invention is directed to this goal.